Internal combustion engines combust an air/fuel mixture to drive pistons that rotatably turn a crankshaft to generate drive torque. The drive torque is transferred from the crankshaft to a drivetrain to propel a vehicle. Mild hybrid vehicles can be temporarily powered using electric motors, which can allow the engines to be periodically turned off to decrease fuel consumption. One example of a mild hybrid vehicle is a vehicle having an engine and a belt-driven starter generator (BSG). The crankshaft of the engine is coupled to a crankshaft pulley and the BSG is coupled to the crankshaft pulley via a belt. When the engine needs to be restarted after a period of inactivity, the BSG can turn the crankshaft using the belt to restart the engine quickly and smoothly.
A multi-ribbed belt is commonly used on automotive vehicles to transmit power between the engine and accessory components. On a conventional drive, the engine crankshaft pulley drives accessories via one belt or multi belts. A tensioner is usually used when multiple accessories are driven via a belt.
In recent years, motor-generator units (MGU) were implemented to do BSG engine start-stop to provide torque assist to boost engine acceleration and to do recuperation to generate electricity in addition to normal generation usually carried out by an alternator. Significant fuel saving and reduction of exhaust can be achieved by a BSG.
To control tension in two different modes of motoring (MGU driving) and generating (engine driving), a group of tensioner designs are frequently used for BSG drives. The common feature of the design is that the tensioner has two arms which are connected by one spring. These tensioners can control belt tension in both modes: motoring and generating. Since motion of both arms is coupled via one spring, the system 1st frequency is significantly reduced, usually shifted below engine firing frequency at idle speed, and vibration of belt drive is significantly reduced in normal operation rpm range.
However, during engine key start, a belt drive using this type of tensioner exhibits high system vibration when the engine speed firing frequency passes through the reduced system frequency, generating system resonance associated NVH issues. To attenuate system vibration of a belt drive which uses an MGU, special control of MGU torque is needed control MGU motion.
A BSG drive can stand alone to become a mild-hybrid system or work together with an integrated start-generator system (ISG) as a hybrid system. The MGU in a BSG drive generates drive torque, consuming power from a battery, to start the engine or to boost in engine acceleration when the driver accelerates to speed up the vehicle. It also functions as an alternator or generator, applying load torque for generating electricity power to charge the battery: recuperation or normal generation. Recuperation generates high torque load and high electric power typically seen in braking operation and moderate load when the foot of driver is off the pedal.
In driving or generating mode, the torque magnitude from MGU is controlled by a number of factors. For example, higher drive torque in boost operation when the driver accelerates very hard; or higher load torque in recuperation when the driver requires hard braking. There is one common feature: direction of torque from MGU, driving or loading, does not change until the operation demand of the engine is changed by the driver.
The rotary speed of an internal combustion engine fluctuates around its average speed. The fluctuation of engine speed is called angular vibration (AV). For example, a 4-cyl engine runs at 750 rpm average speed may have 60 rpm AV at 25 Hz firing frequency. For normal control of a BSG drive, engine average speed is the primary factor. Engine/vehicle acceleration/deceleration refers to average speed.
The prior art BSG systems are used for torque boost wherein the BSG provides start up torque or additional drive torque to supplement the IC engine torque output.
Representative of the art is U.S. Pat. No. 9,303,571 which discloses a method to determine a desired torque output from an engine system in response to a torque request, the engine system including an engine and a belt-driven starter generator (BSG). The method can include determining a current engine torque capacity. When the desired torque output is greater than the current engine torque capacity, the method can include (i) determining a maximum engine torque capacity, (ii) determining a current BSG torque capacity, (iii) commanding the BSG to operate as a torque generator or a torque consumer based on a difference between the desired torque output and the maximum engine torque capacity and a state of a battery system configured to power the BSG, and (iv) controlling the engine and the BSG to collectively generate the desired torque output at a flywheel of the engine.
What is needed is a controller controlling the motor-generator torque at a frequency greater than 1 Hz such that when the internal combustion engine accelerates the motoring torque is applied to speed the motor-generator rotation and when the internal combustion engine decelerates the load torque is applied to slow motor-generator rotation such that motor-generator rotation is controlled to attenuate a system vibration. The present invention meets this need.